The disclosure relates to heat assisted magnetic recording (HAMR), and particularly to alignment features and assembly methods to improve placement accuracy of a laser Chip-On-Submount Assembly (COSA) on a magnetic recording write head assembly.
Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. Energy assisted magnetic recording (EAMR) or heat assisted magnetic recording (HAMR) technology may be used to increase areal density (AD) of hard disks.
Heat assisted magnetic recording technology requires a laser source to provide additional energy during the data writing process. The energy source normally comes from a semiconductor laser diode chip bonded on a submount assembly which is referred to as the Chip-On-Submount-Assembly (COSA). The COSA is attached to the back of a conventional magnetic head slider and the light energy from the laser diode chip is guided to an air bearing surface (ABS) through a waveguide to heat up the magnetic media. Heat from the laser beam lowers the coercivity of the magnetic medium and enables a write pole to magnetize the media with high density, which helps to realize the magnetic recording process with increased AD.
Efficient coupling of the laser beam with the optical waveguide enables writing data at high density to the disk. A requirement for bonding the COSA to the slider is the accuracy which must be achieved, typically at a submicron level. The bonding process itself can be a eutectic or epoxy type attachment. Accurate bonding helps to ensure that the output of the laser diode is aligned to the entry point of the waveguide attached to the slider. The alignment accuracy defines the amount of energy channeled into the waveguide and therefore an efficiency of the whole assembly. When the alignment is poor, more energy is needed from the laser diode to ensure sufficient energy is channeled through the waveguide. Poor alignment leads to low energy efficiency and potential degradation of laser life due to higher required output.
Submicron bonding accuracy presents a significance technological challenge to achieve high speed bonding. Conventionally, there are two methods to achieve high accuracy bonding (submicron). One is passive alignment method which relies on alignment markers and the other is active alignment. In the active alignment method, the laser diode is powered up and the alignment position is searched by scanning the laser diode beam across the waveguide area to identify the optimum position.
A requirement for passive alignment is the visibility of alignment markers on the slider and COSA device. For reliable passive alignment, vision recognition and detection via a high resolution camera requires high contrast between alignment markers and the surrounding regions of the COSA and slider. However, in prior systems, it is difficult for the high resolution camera to properly recognize and detect the markers because of the reflection/interference caused by other components near the markers. A significant problem with conventional marker design is due to the interference of background features which may seriously affect machine vision marker location recognition. The transparent alumina may also contribute to the interference of the background features. The degree of interference may increase with increasing alumina thickness. For example, with a slider thickness of 172 um, the background feature interference appears with brightness comparable to the actual alignment markers, and may seriously impact the machine vision's capability to correctly recognize the alignment markers.
Hence there is a need in the art of passive alignment for methods and structures to facilitate alignment of the laser COSA with the optical waveguide to obtain an optimized optical energy coupling using machine vision recognition.